FIG. 1 is a block diagram of a prior art finger identification device A to verify fingerprints. Fingerprint identification device A includes a fingerprint reader unit 1 including an optical read-in system 3 and a photoelectric converter element 7, and an operation processing unit 2.
FIG. 2 shows a configuration of the fingerprint reader unit 1. Optical read-in system 3 consists of a light source 4, such as a light-emitting diode or the like; a triangular prism 5, to which a person's finger f is applied, and which selectively emits light in an optical pattern corresponding to the pattern of the fingerprint; and a condensing lens 6. Photoelectric converter element 7 generates binary electrical signals which correspond to the optical pattern focussed by condensing lens 6. The photoelectric converter element 7 might, for example, consist of a Charge Coupled Device (CCD).
In the fingerprint reader unit 1, when a finger f, which is the object of investigation, is placed on the oblique surface of the prism 5, the light from the light source 4 which enters the prism 5 is totally reflected by the surface of the prism in conjunction with the grooves of the fingerprint (or print). This reflected light travels toward the lens 6. At the ridges of the print, the light passes through the oblique surface of prism 5 and is scattered by the print. In other words, the light is totally reflected by the grooves of the fingerprint and creates the light portion of the image, while the light is scattered by the ridges of the print and creates the dark portion of the image. The light from light source 4 is thus selectively reflected by the oblique surface of prism 5 in a pattern of light and dark portions which exactly matches the fingerprint pattern. The optical pattern of light and dark portions which is reflected by prism 5 is condensed by the condensing lens 6 and focussed on the photoelectric converter element 7. The optical pattern focussed on element 7 is converted by element 7 into binary electrical signals which are then output, as image data representing the pattern of the fingerprint, to the operation processing unit 2.
As can be seen in FIG. 1, the operation processing unit 2 consists of an image data processing unit 8, a feature extraction unit 9, a comparison unit 10 and a database unit 11. Image data processing unit 8 executes various processing routines such as correcting and compressing the image data transmitted from photoelectric converter element 7. Based on a specified algorithm known to those skilled in the art, feature extraction unit 9 extracts features from the fingerprint pattern (i.e., the image data) processed by image data processing unit 8. For example, it might use the scheme disclosed in Japanese Patent publication 5-54129. Database unit 11 records, prior to use, the fingerprint data (e.g., the feature count) for legitimate or authorized users of the device. Comparison unit 10 compares the fingerprint data (e.g., the feature count) extracted by feature extraction unit 9 with the data (or count) for the authorized users which are recorded in the database unit 11 and determines whether or not they match.
If comparison unit 10 determines that the fingerprint data matches, it outputs judgment data indicating that the match was successful, and a specified operation is executed (for example, the door is unlocked and the person is granted entry, or the car engine is started). If the match is not successful, comparison unit 10 outputs judgment data indicating that it has failed to find a match, and the specified operation is prevented.
With this sort of fingerprint identification device, it sometimes occurs that judgment data indicating a successful match is not output even though the user whose finger is on the read-in unit is an authorized user. In this case, the specified operation is prevented. If this sort of failure occurs frequently, the device needs to be repaired, and someone needs to ascertain where the malfunction is occurring.
Failures of this sort may be due to a number of causes. The prism of the read-in unit may be scratched; the person's finger may be dirty; or there may be foreign matter stuck to the read-in unit or the finger. If any of these things happen, they may cause a problem in the data compression routine used by the image data processing unit to compress the fingerprint pattern, or the features which distinguish one individual's pattern from another's may be difficult to extract, or a problem may occur in the comparison program.
Therefore, such prior art devices to identify fingerprints require much time and effort to determine the cause and the location of a malfunction before any repairs could be made.